The present invention relates to an image receptor and a thermal transfer ink sheet. More particularly, it relates to a thermal transfer ink image receptor which is advantageously used especially with a so-called "tape printer", and to a thermal transfer ink sheet which is advantageously used to form printed images on such an image receptor.
The above-noted tape printer is provided with simple word processing function and printing function, and adapted to form printed images while rewinding an image receptor in the form of a tape which is wound into a pancake-like body. A portion of the image receptor in which the printed images are formed is cut off and the cut piece is stuck onto an object. With the tape printer it is possible to form a heading-printed label, name-printed label and the like with ease.
A thermal transfer printer is usually employed in a printer part of the tape printer because it can be easily scaled down. Therefore, an ink sheet to be used therein is a thermal transfer ink sheet.
As the image receptor in the form of tape (hereinafter referred simply to as "image receptor") for use with such a tape printer, there is known an image receptor of the type wherein on one side of a foundation film such as polyester film is provided an image receiving layer such as made of a polyester resin which allows a thermal transfer ink to exhibit a good fixing property, and on the other side of the foundation film is provided a pressure-sensitive adhesive layer, on which a separator is further stacked (hereinafter referred to as "first prior art"). With this image receptor, an image is formed on the image receiving layer, the separator is then exfoliated, and that portion of the receptor tape in which the image is formed is stuck at its pressure-sensitive layer side on an object.
However, there arises a problem that if this image receptor is stored in the form of pancake, a blocking phenomenon is likely to occur such that the image receiving layer and the pressure-sensitive adhesive layer adhere to each other. Because of the blocking phenomenon, the image receptor becomes hard to be rewound, or even if it can be rewound, the image-receiving side thereof may be soiled or damaged.
The blocking will not occur if the pressure-sensitive adhesive layer is covered with a separator of which both sides are imparted with a releasing property using, for example, a silicone resin. With such a separator, however, when an image receptor body consisting of a foundation provided with an image receiving layer and a separator are wound around a core in the production of the image receptor, the wound receptor is likely to come out of the core because slipping is excessive between the surface of the image receiving layer and that of the separator.
For this reason the first prior art uses a separator of which only the side in contact with the pressure-sensitive adhesive layer is imparted with a releasing property. Therefore, the first prior art is poor in anti-blocking property.
Such a poor anti-blocking property can be significantly improved if the glass transition point of the polyester resin used in the image receiving layer is raised. However, there appears a drawback that the polyester resin of a raised glass transition point degrades the fixing property of the thermal transfer ink.
With the first prior art, in addition, since the printed image on the image receiving layer is exposed, the fastness (against abrasion, alcohol and the like) of the printed image is poor.
As an alternative prior art, there is known an art (hereinafter referred to as "second prior art") wherein printed images are formed on one side of a transparent tape of plastic film, and an adhesive double coated tape which is usually colored is stuck on the side having the printed images so as to allow sticking of the transparent tape on an object.
With the second prior art, although the printed image is superior in fastness by virtue of protection with the transparent film, a step is needed to stack the adhesive double coated tape over the printed image, which entails a problem that the device according to the second prior art cannot be simplified or reduced in size. Therefore, this prior art is not preferable.
It is an object of the present invention to overcome the problems involved in the aforesaid first prior art by providing an image receptor for a thermal transfer ink which enhances the fixing property of the thermal transfer ink and exhibits a satisfactory anti-blocking property while, at the same time, assuring a printed image of good fastness though exposed, and by providing a thermal transfer ink sheet which is advantageously used to form on such an image receptor a printed image of good fixing property and fastness.
This and other objects of the invention will become apparent from the description hereinafter.